Veritas-bu

Re: [Veritas-bu] Media Tape Writes and Retentions

2009-02-18 12:12:30
Subject: Re: [Veritas-bu] Media Tape Writes and Retentions
From: Ed Wilts <ewilts AT ewilts DOT org>
To: "Jackson, Todd" <c-todd.jackson AT invitrogen DOT com>
Date: Wed, 18 Feb 2009 10:41:35 -0600
On Wed, Feb 18, 2009 at 10:17 AM, Jackson, Todd <c-todd.jackson AT invitrogen DOT com> wrote: 

I have a question concerning LTO tape writes that I need some clarity about.


The first thing to understand is that TAPE retention rarely matters.  What really matters is IMAGE  retention.
 

If you have a Retention of 5 weeks for a policy and you write a job the first day which gives the

Images 5 weeks until expiration. When you write to that tape again on week 2, week 3  …   etc.

You really shouldn't do this especially if the images are for the same server's backups.  If you write 5 weeks of the same server to the same tape, and your tape goes bad, you have no backups. 
 

1) Will each week of writes have a separate 5 week retention?


Remember that it's the images that matter.  So yes, each image expires independently.
 

2) Can the tape be written to again (over week 1 space on tape) by week 6 or will something else happen?


You can only append to a tape.  You will not write over any other part of the tape until all of the images have expired.
 

 3) When the time is unassigned I am assuming that is all backup images expiring. Will the tape be written to as

long as it is in a Library or drive and not write protected ..  every time a segment of images expire on the tape?


When all images have expired, the tape (by default) will move to the scratch pool and be eligible to be reused.

Don't mix retentions on the same tape - this is the default.  Putting one image on a tape with a 5-year retention will prevent you from re-using that tape for 5 years even if the vast majority of the images happen to have a 2-week retention.
    .../Ed

Ed Wilts, RHCE, BCFP, BCSD, SCSP, SCSE
ewilts AT ewilts DOT org
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